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Synthesis and Hydrolytic Degradation of Substituted Poly(DL-Lactic Acid)s
Department of Environmental and Life Sciences, Graduate School of Technology, Toyohashi University of Technology, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan
* Author to whom correspondence should be addressed.
Received: 25 May 2011; in revised form: 27 July 2011 / Accepted: 29 July 2011 / Published: 10 August 2011
Abstract: Non-substituted racemic poly(DL-lactic acid) (PLA) and substituted racemic poly(DL-lactic acid)s or poly(DL-2-hydroxyalkanoic acid)s with different side-chain lengths, i.e., poly(DL-2-hydroxybutanoic acid) (PBA), poly(DL-2-hydroxyhexanoic acid) (PHA), and poly(DL-2-hydroxydecanoic acid) (PDA) were synthesized by acid-catalyzed polycondensation of DL-lactic acid (LA), DL-2-hydroxybutanoic acid (BA), DL-2-hydroxyhexanoic acid (HA), and DL-2-hydroxydecanoic acid (DA), respectively. The hydrolytic degradation behavior was investigated in phosphate-buffered solution at 80 and 37 °C by gravimetry and gel permeation chromatography. It was found that the reactivity of monomers during polycondensation as monitored by the degree of polymerization (DP) decreased in the following order: LA > DA > BA > HA. The hydrolytic degradation rate traced by DP and weight loss at 80 °C decreased in the following order: PLA > PDA > PHA > PBA and that monitored by DP at 37 °C decreased in the following order: PLA > PDA > PBA > PHA. LA and PLA had the highest reactivity during polymerization and hydrolytic degradation rate, respectively, and were followed by DA and PDA. BA, HA, PBA, and PHA had the lowest reactivity during polymerization and hydrolytic degradation rate. The findings of the present study strongly suggest that inter-chain interactions play a major role in the reactivity of non-substituted and substituted LA monomers and degradation rate of the non-substituted and substituted PLA, along with steric hindrance of the side chains as can be expected.
Keywords: substituted poly(lactide)s; poly(2-hydroxyalkanoate); polymerization hydrolytic degradation; thermal degradation
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Tsuji, H.; Eto, T.; Sakamoto, Y. Synthesis and Hydrolytic Degradation of Substituted Poly(DL-Lactic Acid)s. Materials 2011, 4, 1384-1398.
Tsuji H, Eto T, Sakamoto Y. Synthesis and Hydrolytic Degradation of Substituted Poly(DL-Lactic Acid)s. Materials. 2011; 4(8):1384-1398.
Tsuji, Hideto; Eto, Takehiko; Sakamoto, Yuzuru. 2011. "Synthesis and Hydrolytic Degradation of Substituted Poly(DL-Lactic Acid)s." Materials 4, no. 8: 1384-1398.